In general, an image captured by using a wide-angle lens such as a fisheye lens is likely to have larger distortion in a peripheral portion of the image.
FIGS. 1A and 1B illustrate how distortion is corrected in the related art. FIGS. 1A and 1B illustrate an image of a black and white parallel stripe pattern captured by using a wide-angle lens. FIG. 1A illustrates an image before distortion is corrected. It can be seen that the peripheral portion of the image has larger distortion due to optical distortion. FIG. 1B illustrates an image after the distortion is corrected. The distortion in the peripheral portion is removed in the image illustrated in FIG. 1B, but the corrected image becomes unnatural due to magnification of the peripheral portion.
In this respect, there have been proposed a large number of distortion correction techniques for acquiring an image having as natural-looking as possible while correcting distortion.
For example, Patent Literature (hereinafter, abbreviated as PTL) 1 discloses a technique that performs distortion correction so as to acquire natural appearance by using a combination of a function for performing distortion correction and a function for not performing distortion correction.
In addition, PTL 2 discloses a technique that performs distortion correction so as to acquire natural appearance by setting a magnification ratio (conversion function) according to coordinates (X-axis and Y-axis values) of an image cut out from a distorted image, and that performs image conversion by using the magnification ratio.